اثرات تغییر اقلیم بر کارکرد شبکه های آبیاری تحت فشار ( مطالعه موردی: آبیاری قطره ای سد ستارخان، آذربایجان شرقی )

A rising trend of the Earth’s temperature and changes in the associated weather conditions across the globe are referred to as climate change. In the absence of suitable mitigation and adaptation measures, climate change is likely to affect the world’s major sectors, such as agriculture, water resources. Climate change as a result of increase in atmospheric CO۲ concentration and other greenhouse gases may have major effects on crops productivity in future. Climate change has direct impacts on hydrological process such as evaporation by water surface, plants’ transpiration, precipitation and temperature patterns and hence, may alter the crop water requirements. The performance of pressurized irrigation networks that are designed based on the past climate conditions, may be influenced due to the increasing water demand. Because of the increasing water demand, studying the impacts of climate change on water resources is necessary. The main objective of this study is to investigate the climate change effects on the management system and operation emitters’ hours in the pressurized irrigation network of Sattar Khan Dam. Future climate projections of Global Climate Models (GCMs) under different emission scenarios are usually used for developing climate change mitigation and adaptation strategies. However, the existing GCMs have only limited ability to simulate the complex and local climate features, such as precipitation. Furthermore, the outputs provided by GCMs are too coarse to be used in hydrologic impact assessment models, as these models require information at much finer scales. Therefore, downscaling of the GCM outputs is usually employed to provide fine-resolution information required for the impact models. Among the downscaling techniques based on statistical principles, multiple regressions and weather generators are considered to be more popular, as they are computationally less demanding than the other downscaling techniques. In the present study, the performances of a weather generator (called LARS-WG) are evaluated in terms of their ability to simulate the frequency of extreme precipitation events of the current climate and downscaling of future’s extreme events. To predict the climate change based on the General Circulation Models (GCMs), the LARS-WG tool for downscaling was used. The LARS-WG model was used to generate the temperature and rainfall data for future period under emission scenarios of B۱, A۲ and A۱B. By using the LARS-WG and HadCM۳ model with three emission scenarios of A۱B, A۲ and B۱ in ۲۰۵۵ horizon, the temperature and precipitation were investigated. The LARS-WG can be used to synthesize daily data and fill in missing values of a recorded climatic time series. It can also generate data of an ungaged site for the daily climatic parameters, such as precipitation, temperature, and solar radiation (using observed data properties of a neighboring gaged site). It takes the long-term daily information of the climatic parameter of interest as the input for a site. It can also generate the changed climate’s scenarios for a site by perturbing the parameters obtained from the observed data to generate synthetic data, representing future climate change. The CROPWAT software has been employed in order to calculate the irrigation requirement. Further, the generated local climatic data of the future years were used as the CROPWAT model input to estimate the irrigation requirements for subsequent years. The CROPWAT model, developed by FAO Land and Water Management Division (FAO, ۱۹۹۲), is an irrigation management model to evaluate the crop water requirements and irrigation needs. Calculations of crop water and irrigation requirements are carried out with inputs of climatic and crop data. The climatologically data included are maximum and minimum temperature, mean daily relative humidity, sunshine hours, wind speed, precipitation and calculated values for reference evapotranspiration and effective rainfall. The results have shown a rise in temperature and reduction in precipitation. In the other part of the research, based on these predictions, the CROPWAT software has been employed in order to calculate apple irrigation requirement. The results showed that the apple irrigation requirement have increased over baseline under three emission scenarios that are affected by temperature rise and reduced rainfall in the watershed. By increase in temperature and crop water requirement in the basin, and decrease in precipitation, the necessity of the system’s management reforming was determined that increasing the irrigation time is suggested as a possible solution. The results showed that the system operation hours in the watershed over baseline under three emission scenarios, have increased ۱۰.۲۸ percent.